1. Field of the Invention
This invention is in the field of integrated circuit chip packages and more particularly relates to the field of an integrated circuit chip package which is provided with improved means for cooling the chip.
2. Description of the Prior Art
Integrated circuit chips, or dies, are generally packaged as either discrete devices, one chip per package, or as part of a multichip hybrid circuit or a hybrid package. With the degree of integration of chips increasing with time, discrete packages of large-scale integrated circuit chips required a substrate which can provide the necessary number of interconnections so that the package comprising a chip and the circuitry of the substrate can become a significant building block of complex electronic circuits. A development with respect to mounting chips on packages and particularly one that lends itself to automating the process of packaging large-scale integrated circuit chips involves producing a flexible beam lead frame which is laminated to a strip of thin plastic material, such as standard 35 mm film. The input and output terminals on the active face of a chip are bonded to inner lead bonding sites of the leads of a given lead frame. The prior art teaches mounting such an integrated circuit chip on a substrate such as a multilayer printed circuit board by blanking the integrated circuit chip and a portion of its lead from the lead frame and the film segment to which each frame is attached. The outer lead bonding sites of the leads are formed to produce a foot at the free end of the lead. The outer surface of each such foot of a lead is the lead's outer lead bonding site which foot is formed so that its outer lead bonding site is substantially parallel to the active face of the integrated circuit chip but displaced so as to be substantially aligned with the bottom surface, or back face, of the chip. The back face of the integrated circuit chip is metallized so that the back face can be soldered to a metallized chip site on the surface of the substrate simultaneously with the bonding of the outer lead sites of the leads of the chip to outer lead pads of the substrate.
Mounting an integrated circuit chip on a substrate with the active face of the chip encapsulated in a thermosetting plastic which is positioned between the chip and the chip pad of the substrate protects the active face of the chip and the inner lead bonds between the inner lead bonding sites and the input and output terminals of the chip from chemical and physical attack, as well as increasing the mechanical strengths of the inner lead bonds. The thermal conductivity of the thermosetting plastic is improved significantly by including in the thermoplastic material a material that is thermally conductive but electrically a good insulator, such as alumina Al.sub.2 O.sub.3, or beryllium oxide BeO. The so-called flip chip approach to mounting chips on a printed circuit board, however, is not without problems, one of which is dissipating the heat that a chip will produce, the total amount of which, particularly for bipolar integrated circuit devices, tends to increase as the degree of integration increases, so as to maintain the temperature of each integrated circuit chip within its designed operating limits.